BERLIN - Security sources in Germany say they are going to increase the presence of special elite police unit aboard airliners following the recent attempt to blow up a Delta airliner over U.S. skies. Members of this force already provide security aboard German airliners flying to Israel.

GSG9, which provides security on flights, is a unit of the German federal police responsible for counter-terror activities, and is answerable directly to the police and the German interior ministry. It was established in 1973, following the murder of 11 Israeli athletes at the Munich Olympics, to provide a response to complex security situations that the regular German police are not trained to carry out.

The unit's members operate undercover and sit among the passengers.

Two German airlines fly to Israel, Lufthansa and Air Berlin; the latter operates flights from Berlin, Frankfurt and Munich.

The exact number of special security people on the flights is unknown, but is estimated at about 200. This number has apparently remained unchanged since it was decided to establish such a unit in 2001, after the 9/11 attacks.

German experts say that providing security on flights is especially important considering the security problems that have been discovered at airports. The chairman of the German police union, Konrad Freiberg, recently told a local newspaper in Stuttgart that "there is a high and worrisome number of security breaches" at airports in Germany. Freiberg also said that on surprise operations, undercover police are able to sneak many weapons and explosives on board airliners.

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